In power transmission and distribution systems, rapid current rises can occur, such as those occurring during short-circuit conditions. In order to protect the high-voltage power lines against dynamic and thermal stresses which accompany the rapid current rises, the line must be electrically opened or cut-off before the short-circuit current has reached its first peak value if the line is carrying alternating current, or before the line has reached its final value if the line is carrying direct current. The cut-off time required, which depends upon the frequency of the alternating current and on the inductance, capacitance and resistance of the power line, should not exceed a few milliseconds. Such rapid cut-off times, however, cannot be obtained with mechanically or magnetically actuated switches in medium-voltage and high-voltage power networks. Therefore, switches have been developed which are actuated by blasting.
One conventional type of blast-actuated switch includes a torsion-rod spring having a contact projecting radially outward from its free end. The switch further includes a pull-rod which cooperates with a lever to place the torsion-rod spring under tension, and to press the elements fastened to the contact onto the main conductor line. The pull-rod has a recess into which a blasting cap is inserted. Upon the occurrence of a short circuit, the blasting cap is exploded, thereby causing the pull-rod to be torn apart. The lever is released and the contact elements are lifted away from the main conductor line as the torsion-rod spring contracts.
Another conventional type of blast-actuated switch includes a casing having a conductor arranged therein. The conductor includes a recess which accommodates a blasting cap. When the blasting cap is exploded, the conductor is directly torn apart.
Such conventional blast-actuated switches, however, have certain disadvantages. In the first mentioned type, the blasting cap is located outside of the region of the electric contacts and therefore does not influence the contacts directly. The separation of the contacts is accomplished exclusively by the spring force of the torsion-rod spring. Consequently, a significant time delay is experienced before the contacts are actually separated.
The second mentioned type of switch provides for a much shorter time delay than that of the first type. However, in the second type of switch, the gaseous materials emitted from the blasting cap as the cap explodes tearing apart the conductor, substantially lower the breakdown voltage across the ends of the blasted conductor, thereby substantially lowering the dielectric strength of the switch.
It is therefore an object of the present invention to provide a high-voltage, blast-actuated power switch in which the contacts are separated without auxiliary mechanical means, and in which the gaseous materials generated by the explosion of the blasting cap essentially does not penetrate the area between the separated contacts.